1. Field of the Invention
This invention relates to a self-bonding magnet wire.
2. Description of the Prior Art
In recent years, users have increasingly demanded self-bonding magnet wires as windings which can permit the omission of or simplification of a varnish-impregnating step in the production of electric machinery and appliances to solve the problem of environmental pollution and the problem of safety and sanitation in working areas, and which can contribute to a shortening in the manufacturing process and a reduction in the cost of production.
Self-bonding magnet wires are used as deflection yoke coils for television sets, and also have various other applications, for example, in various transformers, speakers and motors. As a result, it has been desired to develop materials having various characteristics which conform to the manufacturing processes, the treatment conditions and the service conditions established by the individual users.
Investigation of the chemical nature of materials and the blending of various materials would be a first approach in exploring materials which meet the various requirements of users. However, since the quantities of materials for self-bonding magnet wires are very small as compared with various common plastics, even if a preferred chemical composition exists, it is uneconomical, and in many cases, virtually impossible, to produce a new material only for that use. The general practice, therefore, is to develop materials meeting the required characteristics by blending various commercially available materials which have other uses.
Polymers, however, are frequently difficult to blend because their compatibility or miscibility is unsatisfactory. Moreover, since commercially available polymers have high molecular weights and high solution viscosities, a large amount of solvent must be used, and this often is economically disadvantageous.
Deflection coils for television sets, which are now in use, are produced by winding a self-bonding magnet wire in a yoke coil form with an automatic winder, and pressing and electrically heating the coil to bond the bonding layer on the outside of the insulation coating on the wound wire and to form a yoke coil. Polyvinyl butyral is one example of the materials heretofore used as a bonding layer of a self-bonding magnet wire.
Since the angle of deflection of deflection yoke coils for television has been increased in recent years, a yoke coil must have reduced deformation on heating, and retain its adhesiveness even at high temperatures of, for example, about 130.degree. C. Conventional self-bonding magnet wires using polyvinyl butyral as a bonding layer have the defect that their thermal properties are poor, and thus the requirements described above cannot be met by using polyvinyl butyral.
In an attempt to remove this defect, the addition of a thermosetting resin such as a polyester resin, an epoxy resin or a phenolic resin or a combination of such a thermosetting resin and a blocked isocyanate as a curing agent has been a technique which has been employed. If a small amount of such a thermosetting resin is added, the effect of improving the thermal characteristics is small. If the amount is increased in an attempt to greatly improve the thermal characteristics, the inherent defects of thermosetting resins appear. Specifically, thermosetting enamels are sensitive to the baking conditions employed. If the baking is insufficient, the flexibility of the coated film is reduced markedly. If, on the other hand, the baking is excessive, the bondability of the film is lost or the film requires very high bonding temperatures. Hence, it is difficult to produce products with consistent quality.
In order to meet the requirements described above, polyamide resins have been extensively studied as bonding resins of self-bonding magnet wires for deflection coils. When homopolyamides such as nylon-6 or nylon-6,6 are used, their bonding temperatures are too high because of their high melting points. Bonding at such high temperatures not only accelerates the heat deterioration of the polyamide resins, but also adversely affects the insulation film in an underlayer present. Nylon-12 which has the lowest melting point among homopolyamide resins now commercially produced still has too high a bonding temperature. In order to permit bonding at lower temperatures than those possible with nylon-12 and to retain high adhesiveness at high temperatures of, for example, 130.degree. C., a method was employed of blending two types of copolyamides, as described in Japanese Patent Application (OPI) No. 49488/76. Where a mere blend of two or more copolyamides is used, if the proportion of one copolyamide is larger than those of the other copolyamide(s) the resin film obtained by coating and baking the blend has a comparatively good appearance. However, if the proportions of the copolyamides are about the same, the resin after coating and baking forms a non-uniform film, and the resulting wire insulation has a very good appearance with the formation of raised and depressed portions, peeling, cloudiness or non-uniform or uneven colors. Consequently, the wire tends to deteriorate during winding, and the coil obtained by winding has a poor space factor with the spaces between the wires being too large. Moreover, the flow of the resin is poor and the resin does not bond sufficiently. In particular, the shape of coils cannot be firmly maintained in deflection coils for television sets, and a problem of color shearing occurs. Hence, the wire is not practical as a self-bonding magnet wire.
Such an enamel is a uniform clear solution, and the resin film obtained as a self-bonding layer is very thin. It has been found that when the enamel is coated and baked on a transparent material such as a glass sheet, the resulting resin film is non-uniform and non-transparent and depressed and raised portions and peeling are formed because of the lack of miscibility of the constituent components used. This is not clearly seen with conductors such as copper or aluminum because they are opaque to light. Thus, it has been found that when a enamel composed of a solution of a mere blend of copolyamides is used, the formation of raised and depressed portions and peeling on the film of the resulting self-bonding magnet wire is due to the poor miscibility of the resins in the film obtained by baking the enamel. Furthermore, since an enamel composed of a mere solution of at least two copolyamides in a solvent has a high viscosity and a low concentration, large amounts of solvent and thinner must be used. This is not only uneconomical, but also decreases the coatability of the enamel.